The present invention relates to a fuel injector assembly, and an internal combustion engine containing such a fuel injector assembly. The fuel injector assembly of the present invention includes a piezoelectric actuator and a hydraulical amplifier for operating a control valve to disperse fuel.
Modem Diesel engine design faces the dilemma of providing substantial fuel economy yet meeting increasingly more stringent emission regulations. In an effort to meet these objectives, Diesel engines have been provided with electronic controlled unit injector technology integrated with solenoid actuated control valves. Such integration has been attempted in an effort to provide precise control of the dispersing of fuel at the beginning and the end of fuel injection. The objectives have been to thereby provide precise control of fuel injection timing and quantity to improve fuel economy and emission performance.
Combustion theory and engine test results indicate that the fuel injection rate of a Diesel engine strongly affects emission and fuel economy. In general, a low injection rate during the first half of fuel injection tends to yield low NOx emission, and a higher injection rate during the second half of fuel injection appears to improve fuel economy and reduce particulate emission. Providing satisfactory fuel economy and emission performance is further complicated in that at different engine speed and load, the desirable fuel injection rate shapes are different. For a conventional electronic controlled unit injector, the fuel injection pressure versus time is a triangular shape, and the fuel injection rate is a trapezoidal shape. In a conventional electronic controlled unit injector, the initial rate is determined by needle valve open pressure and needle valve motion. The main injector rate buildup is relatively linear from the initial rate to a high rate near the end of injection. To meet the more stringent emission regulations, the next generation Diesel engine requires an additional degree of freedom in engine control whereby injection rate shape is adjusted electronically.
Efforts have been made to improve control valve response, and thereby improve the capability to control injection rate shape, by the application of piezo material for the control actuator of a Diesel fuel injector. Examples of the use of piezoelectric elements in the control of fuel injection include U.S. Pat. Nos. 5,630,550; 5,697,554 and 5,779,149 to Kurishige et al., Auwaerter et al. and Hayes, Jr., respectively.
An object of the present invention is to provide an improved fuel injector assembly.
Another object of the present invention is to obviate the disadvantages of the prior art by providing an improved fuel injector assembly.
Yet a further object of the present invention is to provide an improved fuel injector assembly which provides improved fuel economy and emission performance.
A further object of the present invention is to provide an improved electronic controlled unit fuel injector assembly wherein a control valve is controlled by a piezoelectric actuator and hydraulic amplifier.
Yet another object of the present invention is to provide an internal combustion engine which includes an improved fuel injector assembly which achieves one or more of the above objects.
This invention achieves these and other objects by providing a fuel injector assembly which comprises an injector body having a fuel inlet and a spill port and which is structured and arranged to disperse fluid fuel. An injector nozzle assembly is provided which is attached to the injector body and is structured and arranged to disperse fluid fuel from the injector body to a combustion chamber. A plunger is disposed within the injector body and is structured and arranged for reciprocating movement to pressurize fluid fuel within the injector body and injector nozzle assembly to disperse fluid fuel from the injector nozzle assembly to the combustion chamber. A control valve is provided which is associated with the injector body and is structured and arranged to direct the flow of fluid fuel between (a) the fuel inlet and the spill port in an open mode and (b) the fuel inlet and the injection nozzle assembly and fuel outlet to disperse fluid fuel to the combustion chamber in a closed mode. A piezoelectric actuator is provided which is associated with the injector body and is structured and arranged for excitation by a variable voltage component so that axial dimension of the piezoelectric actuator is changed upon such excitation. A hydraulic amplifier is provided which is structured and arranged to magnify such axial dimension and thereby permit opening and closing of the control valve in the open mode and the closed mode, respectively. The hydraulic amplifier comprises a first piston coupled with the piezoelectric actuator, a second piston coupled with the control valve, and a hydraulic fuel chamber therebetween. The first piston is larger than the second piston. A pressure check valve is provided which is structured and arranged to selectively supply fluid fuel from the fuel inlet to the hydraulic fuel chamber. The fluid fuel in the hydraulic fuel chamber is (a) pressurized between the first piston and the second piston, when the piezoelectric actuator is excited, to close the control valve in the closed mode, and (b) depressurized, when said piezoelectric actuator is not excited, to permit opening of the control valve in the open mode. An internal combustion engine including such a fuel injector assembly is also provided.